Floating wind turbine platform with ballast control and mooring system

ABSTRACT

A floating wind turbine platform includes stabilizing columns, a tower, water-entrapment plates connected to the stabilizing columns, and a ballast control system. The tower is mounted over one of the columns. The stabilizing columns include internal volumes for containing a ballast. The ballast control system includes an alignment sensor and a controller. The alignment sensor is configured to detect a rotation of the tower. The controller is configured to direct a transfer of ballast from one column to another column to adjust an alignment of the tower.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 13/925,442, filed Jun. 24, 2013, now U.S. Pat. No. 8,692,401which is a continuation of U.S. patent application Ser. No. 12/988,121,filed Oct. 15, 2010, now issued as U.S. Pat. No. 8,471,396, on Jun. 25,2013, which is a national stage application of PCT Patent ApplicationNo. PCT/US2009/039692, filed Apr. 6, 2009, which claims priority to U.S.Provisional Patent Application No. 61/125,241, titled “Column-StabilizedOffshore Platform With Water-Entrapment Plates And Asymmetric MooringSystem For Support Of Offshore Wind Turbines” filed Apr. 23, 2008, theentire contents of which are hereby incorporated by reference.

BACKGROUND

A wind turbine is a rotating machine which converts the kinetic energyfrom the wind into mechanical energy that is then converted toelectricity. Wind turbines have been developed for land basedinstallations as well as offshore installations. The land based windturbines are fixed to the ground and located in windy areas. There arevertical axis wind turbines that have the main rotor shaft arrangedvertically and horizontal axis wind turbines that have a horizontalrotor shaft that is pointed into the wind. Horizontal axis wind turbinesgenerally have a tower and an electrical generator coupled to the top ofthe tower. The generator may be coupled directly or via a gearbox to thehub assembly and turbine blades.

Wind turbines have also been used for offshore applications. Singletower offshore systems are mounted into the sea bed and limited toshallow water depths up to 30 meters. If the turbine tower is mounted ona wider base, such as a lattice structure, this shallow depthrequirement can be extended to 50 m. In deeper water, only floatingsystems are expected to be economically feasible. The drawback ofshallow water systems is that the water is typically only shallow closeto shore. Thus, wind turbines close to shore can block the shore viewand create navigational obstructions and potential hazards for watervessels and aircraft.

Currently, there are a number of concepts for offshore floating windturbine platforms being developed. Generally, these fall into three maincategories: Spars; Tension Leg Platforms (TLP's); andsemi-submersible/hybrid systems. Examples of floating wind turbineplatforms include the Statoil Norsk-Hydro Hywind spar, (FIG. 1), theBlue H TLP recent prototype (FIG. 2), the SWAY spar/TLP hybrid (FIG. 3),the Force Technology WindSea semi submersible (FIG. 4) and theTrifloater semi submersible (FIG. 5). With reference to FIG. 1, sparsare elongated structures that are weighted with significant ballast atthe bottom of the structure and buoyant tanks near the waterline. Forstability purposes, the center of gravity must be lower than the centerof buoyancy. This will insure that the spar will float upright. The sparis moored to the sea floor with a number of lines that hold the spar inplace. In general terms, spar type structures have better heaveperformance than semi-submersibles due to the spar's deep draft andreduced response to vertical wave exciting forces. However, they alsohave more pitch and roll motions than the other systems, since the waterplane area which contributes to stability is reduced in this design.

With reference to FIG. 2, TLPs have vertically tensioned cables or steelpipes that connect the floater directly to the sea bed. There is norequirement for a low center of gravity for stability, except during theinstallation phase, when buoyancy modules can be temporarily added toprovide sufficient stability The TLPs have very good heave and angularmotions, but the complexity and cost of the mooring installation, thechange in tendon tension due to tidal variations, and the structuralfrequency coupling between the tower and the mooring system, are threemajor hurdles for TLP systems.

When comparing different types of offshore wind turbine structures, waveand wind induced motions are not the only elements of performance toconsider. Economics play a significant role. It is therefore importantto carefully study the fabrication, installation,commissioning/decommissioning costs and ease of access for maintenancemethodologies. Semi-submersible concepts with a shallow draft and goodstability in operational and transit conditions are significantlycheaper to tow out, install and commission/decommission than spars, dueto their draft, and TLPs, due to their low stability before tendonconnection.

SUMMARY

Semi-submersible offshore floating wind turbine platforms that includeat least three columns are described herein. In addition to at leastthree columns, the wind turbine platforms described herein includeadditional features that improve the performance of the wind turbineplatform. In an embodiment represented in FIG. 6, the floating windturbine platform includes an active ballast system that moves waterballast between the columns to keep the tower vertically aligned.Moreover, an alignment sensor can be coupled to the platform todetermine the wind loading. Even further, wind turbine platformaccording to the present description may include one or more additionalfeatures, such as an asymmetric mooring system and an active ballastsystem that facilitate production of a structure that can not onlywithstand environmental loads, but is also relatively light weight whencompared to other platform designs and can lead to better economics forenergy production.

The columns included in the platforms described herein can be coupled toeach other with a tubular truss system that includes horizontal andvertical bracing beams. A horizontal water-entrapment plate is attachedto the bottom portion of some or all of the columns. The wind turbinetower is subjected to considerable wind loads very high on thestructure, and spacing between columns achieves stability. In anembodiment, as illustrated in FIG. 6, the turbine tower is attached tothe top of one of the columns, which is itself coupled to the othercolumns by the main beams. This construction improves the structuralefficiency of the floating wind turbine platform and allows thestructure to be of a relatively light weight.

In another embodiment, illustrated in FIG. 7, the turbine tower iscoupled directly above a buoyancy column that supports the weight of thetower and wind turbine components. In this embodiment, the other columnsfunction to stabilize the platform and keep the tower in a verticalalignment. Further, an active buoyancy system can be used to moveballast between the columns. In the embodiment shown in FIG. 7, becausethe weight of the tower is not supported by the buoyancy of the outercolumns, the platform does not require as much structural supportbetween the outer columns and the center tower column. In contrast, insome previous designs where the tower is positioned at the center of thedeck, the structure is relatively heavy and potentially lesseconomically feasible because, due to the weight of the tower andturbine and the aerodynamic moment, the structure must support largeloads at the middle of a long structure.

A nacelle, which can house, for example, one or more of a pitch controlsystem, gear box, yaw controller and generator, can be mounted on top ofthe tower and provides support to the hub and turbine blades that extendfrom the hub. The hub can include a mechanism that allows the pitch ofthe turbine blades to be adjusted so that the rotational speed of theturbine blades is constant over a normal wind speed range. The nacellecan be coupled to a yaw control system, which points the turbine bladesdirectly into the wind for optimum efficiency. Wind turbine equipment,such as the gear box and electrical generator, that are typicallypositioned within the nacelle may reside there, or they may bepositioned lower in the tower or on top of column. Direct driveturbines, which do not have a gear box, may also be used with theplatforms described herein. The electrical power produced by thegenerator can be in a random frequency and amplitude due to the variablewind speed. The electrical power can be altered with a transformer,inverter and a rectifier to produce a uniform output voltage andcurrent. These electrical components can be located in the nacelle, atthe bottom of the tower or on another column. The electrical output fromthe wind turbine can be transmitted through an electrical cable thatruns to the sea floor and a power station. Rather than running straightto the sea floor, a portion of the cable can be coupled to buoyancymechanisms that elevate the portion of the cable. The cable may thenhave a curved path, which allows the floating wind turbine platform tomove vertically or horizontally with the waves, current and tideswithout putting any significant additional tension on the cable.

In an embodiment, the floating wind turbine platform has a specialconfiguration that is a high strength structure. The main beams mountedbetween the columns are equal in length and form substantially anequilateral triangle. Horizontal bracing cross beams are coupled betweenthe adjacent main beams at approximately one third the length of themain beams. The horizontal bracing cross beams and main beams formadditional equilateral triangles at the three corners of the triangleformed by the main beams. Vertical bracing beams are coupled between themid sections of the columns and one third the length of the main beams.The triangles formed by the vertical bracing beams, columns and mainbeams are substantially right isosceles triangle. This configurationprovides a strong structure that can support the required load forceswhile minimizing the amount of material to build the floating windturbine platform.

In specific embodiments, a floating wind turbine platform as describedherein can be designed to be fabricated and assembled entirely atquayside. For example, a crane can be used to assemble components of thefloating wind turbine platform that can be completely constructed at thequayside assembly site. Additionally, where desired, the wind turbinecomponents can be assembled and integrated with the platform andsubstructure at quayside. Once fully assembled, the ballast can becompletely removed from the columns of the floating wind turbineplatform so the structure can be floated out of a channel to theinstallation site. If additional buoyancy is needed to reduce the draftto get out of a channel, a buoyancy module can be attached to one ormore of the columns to reduce the draft. Once the platform has reacheddeeper water, the buoyancy module can be removed and the columns can bepartially filled with water ballast to stabilize the platform.

Sea anchors can be secured to the sea floor prior to towing the floatingwind turbine platform to the installation site. When the floating windturbine platform is moved into position, the mooring lines can befastened to the columns and tightened to a predetermined tension. In anembodiment, the tower is mounted over one of the columns and the mooringlines are arranged in an asymmetric manner, with more of the mooringlines coupled to the column supporting the turbine tower than to theother columns. For example, if four mooring lines are used, two of theselines are connected to the column supporting the tower at anapproximately 90-degree angle interval and one line is connected to eachof the remaining columns. By way of another example, if six mooringlines are used, four mooring lines can be connected to the towersupporting column at approximately 60-degree angle intervals about a 180degree range and each of the other columns is coupled to a singlemooring line. The angles of the mooring lines can be configured tointersect at the tower column. If a symmetric floating wind turbineplatform is used, the mooring lines can be coupled to the platform in asymmetrical manner. For example, a total of six mooring lines can beused with two mooring lines coupled to each of the columns.

The mooring lines can be conventional catenary-shaped lines composed ofa combination of chain, wire ropes and drag-embedment anchors.Alternatively, the mooring lines can be composed of taut polyestersections, and also include clump weights, which are heavy massessuspended to sections of the mooring system. In an embodiment, theanchors are embedded into the sea floor and a section of chain iscoupled to the anchors. Polyester line can be attached to the chain toprovide some elasticity to the mooring line. Where used, the oppositeend of the polyester line can be coupled to an additional length ofchain that is attached to one or more tensioning mechanisms on each ofthe columns. Heavy clump weights can be attached to the chains that areconnected to each of the columns to lower the angle of the chains to thecolumns, and the mooring lines can be tensioned by mechanisms coupled toeach of the columns.

If the wind turbine and tower are mounted on one of the three columns,one column supports more weight and the hull is asymmetrically balancedwhen there is no wind. However, the wind force against the turbineblades and tower cause a moment against the tower that normally pushesthe tower away from the center of the platform. This moment applies adownward force on the tower supporting column while reducing thedownward force on the independent columns that do not support the tower.

When the wind turbine is installed, the wind turbine will spin and thegenerator will produce electricity. However, the wind speed anddirection can change frequently. Therefore, in certain embodiments, aturbine utilized on a platform according to the present description canbe provided with a wind direction system including a wind directionsensor and a yaw control system. In such an embodiment, the winddirection sensor will detect shifts in the wind direction and the yawcontrol system will rotate the nacelle (yaw) at the top of the tower toalign the turbine blades with the wind direction. Even further, aturbine utilized on a platform according to the present description canbe provided with a wind speed sensor that detects changes in the windspeed and is coupled to a turbine pitch control system that responds tochanges in wind speed by inducing a change in the pitch of the turbineblades to optimize the output power or minimize the wind drag forces onthe turbine blades. Examples of commercially available wind directionand speed sensors are available from Campbell Scientific Ltd., UnitedKingdom and NovaLynx Corp., USA.

As the wind speed increases against the tower and turbine blades, thewind force can cause the entire floating wind turbine platform to leanout of vertical alignment. In order to compensate for the wind forces(thrust), a wind turbine platform according to the present descriptionis provided with an internal ballast system that utilizes water pumps tomove water between each of the columns. In an embodiment, the internalballast system includes one or more alignment sensors coupled to acontroller that controls the water pumps of the ballast system. If analignment sensor detects that the floating wind turbine platform isleaning towards one of the columns, the internal ballast system can pumpwater out of the low floating column and into the other columns toincrease the buoyancy of the low column and reduce the buoyancy of theother columns. This water movement will raise the low floating corner ofthe platform so that the tower is returned to a vertical alignment. Whenthe alignment sensor detects that the vertical alignment isre-established, the pumps can be stopped. Because it is only necessaryto compensate for over-turning moment applied to the structure, in oneembodiment of the internal ballast system, there is no need to pumpadditional water from the outside, and the internal ballast system canfunction in a closed loop.

Because operation of the internal ballast system requires pumping of asubstantial amount of water, the response time for achieving a desiredballast adjustment may be as long as 15-30 minutes. In an embodiment,the alignment sensor can be two gyroscopes that can sense rotationalmovement about the X and Y axis in the horizontal plane. In perfectvertical alignment, the X and Y axis gyroscopes will not detect anyrotation of the platform. However, if there is any tilting of thefloating wind turbine platform, the X and/or Y axis gyroscopes candetect rotational movement. Such an alignment sensor can be coupled to acontroller that responds to the misalignment by pumping water to thecolumns as necessary to correct the vertical alignment error. In anembodiment, the ballast system is a closed system that completelyisolates the ballast water from the surrounding sea water. In such anembodiment, because the seawater cannot enter the columns, the columnscannot be flooded and the platform cannot capsize due to a malfunctionof the ballast system.

In an embodiment, the turbine control system and the ballast system arecoupled so the tower can be vertical but the ballast pump may still needto function until the turbine is in an optimal power production mode. Inthis case the turbine blade pitch is modified to reduce the thrust andkeep the mast vertical. The blade pitch can then be slowly rotated backto its optimal angle as the ballast water is pumped from one column tothe next.

The wind turbine platforms described herein can be used as a standaloneplatform or, alternatively, the platforms described herein can bepositioned as part of a plurality of floating wind turbine platformsarranged in a wind farm. The electrical power from each of the windturbines can be combined and transmitted through a single cable towardsa power station which can be on land or on a separate floating platform.In one such embodiment, one of the platforms can be used for crew ormaintenance quarters. This can provide a safe sheltered area whereworkers can be protected from severe ambient weather conditions.

If a floating wind turbine platform as described herein needs to bereturned to docks for servicing or decommissioning, the platform can bedisconnected from the mooring lines and power cable and towed to thequayside assembly site. In shallow water channels the fixed waterballast can be pumped out so the platform draft is reduced to itstransit draft. If necessary, one or more buoyancy modules can be coupledto the columns if the transit draft needs to be further reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a spar type floating wind turbine platform;

FIG. 2 illustrates a tension leg floating wind turbine platform;

FIG. 3 illustrates a tension leg/spar floating wind turbine platform;

FIG. 4 illustrates a symmetric semi submersible floating wind turbineplatform;

FIG. 5 illustrates a perspective view of an asymmetric semi submersiblefloating wind turbine platform;

FIG. 6 illustrates an asymmetric semi submersible floating wind turbineplatform;

FIG. 7 illustrates an elevation view of a semi submersible floating windturbine platform;

FIG. 8 illustrates a top view of a semi submersible floating windturbine platform;

FIG. 9 illustrates a water-entrapment plate connected to the bottom ofthe floating wind turbine platform;

FIG. 10 illustrates a top view of the asymmetric semi submersiblefloating wind turbine platform;

FIG. 11 illustrates a top view of the asymmetric semi submersiblefloating wind turbine platform;

FIG. 12 illustrates an elevation view of the semi submersible floatingwind turbine platform with a taut mooring line system;

FIG. 13 illustrates an elevation view of the semi submersible floatingwind turbine platform with a catenary mooring lines system;

FIG. 14 illustrates a diagram of the ballast control system;

FIGS. 15-17 illustrate an elevation view of the floating wind turbineplatform reacting to changes in wind velocity;

FIGS. 18-20 illustrate an elevation view of the floating wind turbineplatform reacting to changes in wind velocity;

FIGS. 21-23 illustrate sequential steps for moving the floating windturbine platform from quayside to deep water;

FIG. 24 illustrates an arrangement of a group of asymmetric semisubmersible floating wind turbine platforms.

DETAILED DESCRIPTION

Semi-submersible, floating wind turbine platforms are described herein.The platforms described herein can be used, for example, in offshorewind turbine installations. With reference to FIG. 6, wind turbinesystem according to the present description can include an offshoreplatform 105 having at least three columns 102, 103. A planarwater-entrapment plate 107 is attached to the bottom portion of eachcolumn 102, 103. In an embodiment, the columns 102, 103 are cylindricalin shape. However, the columns can be configured in any shape suitablefor constructing a wind turbine platform. A wind turbine tower 111 ispositioned directly above a stabilizing column 102. The two independentstabilizing columns 103 that do not support the turbine tower 111 areseparated by an angle that can range from about 40 to 90 degrees fromthe tower supporting column 102. While the platform 105 shown in theillustrations includes three columns 102, 103, in other embodiments, theplatform can include four or more columns.

The columns 102, 103 are interconnected with a truss structure composedof main beams 115, bracing beams 116 and cross beams 117. The main beams115 are connected to the tops and bottoms of the columns 102, 103 andbracing beams 116 that are connected coupled between the main beams 115and columns 102, 103. The cross beams are connected between the adjacentmain beams 115. In an embodiment, the main beams 115 can be configuredsuch that they intersect with the three columns 102, 103 and form anequilateral triangle. Similarly, the horizontal bracing beams 117 andmain beams 115 can be configured to form additional equilateraltriangles. In an embodiment, the vertical bracing beams 116 are coupledto the columns 102, 103 at approximately the middle of the height andcoupled to the main beams 115 at points that are approximately one thirdthe main beam length. The main beams 115, columns 102, 103 and verticalbracing beams 116 can form right isosceles triangles. In an embodiment,the main beams 115, vertical bracing beams 116 and horizontal bracingbeams 117 are preferably hollow tubular structures of circular orrectangular cross sections. Alternatively, the main beams 115, verticalbracing beams 116 and horizontal bracing beams 117 can also be solid I,H or T beams. In other embodiments the three columns 102, 103, bracingbeams 116 and horizontal bracing beams 117 can form any other types ofgeometric configurations suitable for achieving a platform exhibitingdesired strength, weight, load bearing or other performancecharacteristics.

This design of a floating wind turbine platform as described hereinprovides an strong and efficient structure. The strength can beattributed to the tetrahedron structures formed at corners of theplatform by the columns, main beams, vertical bracing beams andhorizontal bracing beams. A load analysis of the structure shows thatany deformation is most likely to occur in the middle sections of themain beams 115 between the adjacent tetrahedrons. While the geometry ofthe structure is very efficient, the strength of the structure can alsobe increased, for example, by increasing the outside diameter or wallthicknesses of the main beams 115, vertical bracing beams 116 andhorizontal bracing beams 117. If the main beams 115, vertical bracingbeams 116 and horizontal bracing beams 117 are tubular structures, thefatigue life of the structure can be substantially extended byincreasing the wall thickness. For example, if the wall thickness of thetubes is double the nominal tube wall thickness, the fatigue life of thestructure may be increased by approximately 10 to 20 times the fatiguelife of the nominal tube wall thickness structure. Wall thickness may beincreased in a short section near the intersections of main beams 115with the vertical bracing beams 116 and the horizontal bracing beams117.

In an embodiment, the diameter or width of the base of the turbine tower111 approximates but is slightly smaller than the diameter or width ofthe column 102 upon which it is positioned. This uniformity maximizesthe continuity of the structure and minimizes the stress concentrationsin the critical areas of the platform 105 structure. The stressconcentrations can be highest at the junction of the turbine tower 111and column 102 upon which the turbine tower 111 is positioned, wherebending moments are highest due to wind-induced moments and where themain beams 115 connect to the other stabilizing columns 103. In oneembodiment, the diameter of the columns 102, 103 may be uniform tocreate a straight structure, such as a straight cylindrical structure,while the tower 111 can be larger at the base and taper to a smallerdiameter or width at the top. The columns 102, 103 can be constructed bywelding a number of uniform diameter tubular sections together while thetower 111 can be constructed by bolting and/or welding a series oftapered sections together. The columns 102, 103 and the tower 111 can bestrengthened with internal structures such as plates, ribs and internalflanges.

Because the columns 102, 103 only provide buoyancy and stability for thefloating wind turbine platform, only minimal deck space 119 is requiredbetween the tops of the columns 103. Narrow gangways can be placed ontop of the upper main beams 115, connecting each of the columns 102,103. Additional areas on the platform 105 may be used to supportsecondary structures, such as auxiliary solar cells or support of waveenergy converters, and to provide access around the wind turbine tower111. In one embodiment, the decks 119 are positioned on top of one ormore stabilizing columns 102, 103, and the stabilizing column and decks119 are configured such that the highest expected wave crests will notreach or damage the deck equipment or the turbine blades 101. Stairs anda boat docking structure can be attached to any of the columns 102, 103.The platform 105 can be secured to the sea floor by mooring lines131-141 attached to the bottoms of the columns 102, 103.

The turbine blades 101 are long in length and narrow in width having avery high aspect ratio. The turbine blades 101 are connected at theirbase to a hub, a motor and actuators can change the pitch of the blades101. The pitch of the blades 101 can be set to optimize the electricalpower output of the generator. This can be accomplished by adjusting thepitch of the blades to maintain a constant speed of rotation over arange of wind speeds. At lower wind speeds, the pitch of the turbineblades is lower so that they can maintain a maximum rotational speed. Incontrast, at higher wind speeds the pitch is increased to prevent therotation from exceeding the optimum rate of rotation. In order to sensethe true wind speed, the wind turbine can include a wind anemometer thatdetects the wind speed and a controller can adjust the pitch of theturbine blades 101 to the proper pitch angle based upon the detectedwind speed. Commercial turbine blade pitch control systems are availablefrom LTi REEnergy, Germany and Bosch Rexroth, Germany.

Accurately aligning the turbine blades 101 in an orientationperpendicular to the wind direction leads to generation of maximumelectrical power. To facilitate such positioning, the wind turbine mayinclude a wind direction system that includes, for example, a winddirection sensor that detects any misalignment and a yaw control system.Commercial inclination sensors are available from Pepper+Fuches, Germanyand MicroStrain, Inc. USA. If an angular offset is detected by the winddirection sensor, the controller can actuate a yaw motor that rotatesthe nacelle, hub and turbine blades 101. In an embodiment, the turbineblades 101 and hub are coupled to a gear box that increases therotational speed of the turbine blades 101 to a speed suitable forgenerating electricity. The gearbox increases the rotational speed of adrive shaft that is coupled to a generator which produces electricity.In another embodiment, a direct drive turbine is used. There is nogearbox and the drive shaft is coupled directly to the generator, whichmay reside in the nacelle or in the tower.

The electrical output generally increases with wind speed. However, aminimum wind velocity of about 3 meters per second is typically requiredto cause the turbine blades to rotate. For a typical wind turbinegenerator, power output will continue to increase with increases in windspeed up to about 12 meters per second, and in a wind range of windspeeds 6-12 meters per second, the turbine blades are pitched tooptimize the electrical energy production. At wind speeds higher than 12meters per second, the turbine blades of a typical wind turbinegenerator are adjusted to control the lift force and let the turbinerotate at its optimum speed, hence maintaining the maximum power output.A 5 megawatt turbine generator may reach a maximum power output at awind speed of about 12 meters per second. At higher wind speeds betweenabout 12 to 25 meters per second, the generator will produce 5 megawattsof electrical energy, but the turbine blades are rotated at a higherpitch angle to reduce the wind force loads on the turbine blades andmaintain the optimal speed of rotation. At wind speeds greater thanabout 25 meters per second, the wind turbine system may be shut down andparked. The turbine blades are adjusted to minimize the wind forces andmay also be locked down until the wind speed drops to prevent overspeedand damage to the wind turbine.

While the floating wind turbine platform has, thus far, been illustratedin an asymmetric tower placement, in other embodiments the tower islocated symmetrically between the columns. With reference to FIGS. 7 and8, a floating wind turbine platform 106 is illustrated with the tower111 located symmetrically between the columns 103. FIG. 7 illustrates anelevation view of the floating wind turbine platform 106, and FIG. 8illustrates a top view of the floating wind turbine platform 106. Inthis embodiment, the tower 111 is mounted over a buoyancy column 104.The buoyancy column can be a hollow structure which provides some or allof the buoyant force required to support the weight of the tower 111,the nacelle 125, the turbine blade 101 and other system components.Because the buoyancy column 104 is mostly hollow and displaces a largevolume of water, it is unstable. In order to stabilize the floating windturbine platform 106, the buoyancy column 104 is coupled to three ofmore stabilizing columns 103 that include a ballast system to stabilizethe tower 111. The floating wind turbine platform 106 can have supportbeams 108 that extend between the stabilizing columns 103 and thebuoyancy column 104 as well as bracing support beams 112 that extendbetween the stabilizing columns 103 and the buoyancy column 104. Otherstructural details of the floating wind turbine platform are the same asdescribed above with reference to FIG. 6.

The wind turbine platforms described herein include one or morehorizontal water-entrapment plates 107 attached to the bases of each ofone or more of the platform columns. The one or more water-entrapmentplates 107 are positioned such that they are submerged. With referenceto FIG. 9, the function of the water-entrapment plate 107 is to providehydrodynamic added-mass and damping. The amount of water “entrained” bya square plate with side length λ moving along its normal direction isapproximately equal to ρλ³ where ρ is the water density. A large amountof entrained water also known as hydrodynamic added-mass is thereforeassociated with a square horizontal plate of substantial dimensionsmoving vertically. A rectangular plate with a large aspect ratio willentrain much less water relative to its area.

The shape and dimensions of the water-entrapment plate 107 are such thatthey cause a substantial increase of the platform added-mass in heaveand added-moment of inertia in roll and pitch. Since the platform draftis relatively shallow, typically 100 feet or less, wave-exciting forceson the water-entrapment plate cannot be neglected. Hydrodynamiccalculations should be conducted to determine the response of theplatform, taking into account the increase in added-mass and waveexciting forces. Commercial diffraction-radiation software, such asWAMIT, may be used to compute floating platform responses. In ahypothetical example, a 15,000 tons displacement platform carrying over7,000 tons payload was considered for these response computations.Without water-entrapment plates, the platform's natural period is around12 seconds, which corresponds to a frequency band with considerableamount of energy during big storms. The resulting resonant responseyields unacceptable platform motion, resulting in damage to the platformstructure. By adding the one or more water-entrapment plates, which, inone embodiment, extend radially outward by about 20 to 30 feet from acolumn base, the platform's heave natural period can be significantlyextended to 20 seconds, which results in acceptable motion response.

Therefore, the one or more water-entrapment plates 107 provided in aplatform as described herein can provide a substantial increase invertical added-mass, while minimizing the increase in wave excitingforce, resulting in a beneficial reduction of platform motion. Such astabilizing effect is especially beneficial for small platforms forwhich suitable performance cannot be obtained merely by adjusting columnsize and spacing. The positioning of the one or more water-entrapmentplates 107, such as the radial distance of a plate from the center of agiven column 102, 103, and the configuration of the one or morewater-entrapment plates 107, such as the total plate area, can beadjusted to achieve, for example, a desired increase in the verticaladded-mass and a reduction or minimization of the increase in waveexciting force.

Due to its size, a water-entrapment plate 107 attracts largehydrodynamic loading including added-mass and wave radiation effects,wave exciting forces and viscous effects due to shedding of vorticesfrom the edges of the plate 107. The plate 107 must be supported byadditional structural members in order to withstand extreme wave loadingas well as fatigue damage due to the large number of wave cycles it issubjected to. In an embodiment, radial stiffeners 179 extend from thecolumns 103 toward the plate's outer edges to support the plate 107.Main beams 115 connected to the columns 103 also provide structuralsupport to the water-entrapment plate 107, as well as rigidity to theoverall structure. Additional plate 107 strengthening components caninclude, for example, girders 181 supported by radial stiffeners 179,stringers 177 between the girders 181 and water-entrapment platebracings 121 mounted between a column 102 and the stiffeners 179. Thesestructural members support the panels forming the water-entrapment plate107. The entrapment plates described herein can be formed of anysuitable material, such as steel.

In order to properly dimension the water-entrapment plate stiffeners,the various hydrodynamic effects taking place on the plate must beproperly accounted for. These consist of the following: inertia of thefluid surrounding the water-entrapment plate causing a force opposingthe acceleration of the platform, particularly in the verticaldirection; radiated waves generated by the platform as it movesresulting in energy being removed from the platform; incident wavesinteract with the platform hull causing forces; and viscous effects,predominantly due to the shedding of vortices from the plate edges alsoresulting in transfer of energy from the platform to the water. Allforces, except the viscous forces, can be modeled based on thediffraction-radiation theory which neglects the fluid viscosity, andrequire numerical solution of the Laplace equation. Viscous effects aredetermined from an empirical model developed with small-scale laboratoryexperiment results. The hydrodynamic forces can be converted to apressure field on the platform's submerged portion, including thewater-entrapment plate, and a structural finite-element model can thenbe run to determine stresses in all structural members includingstiffeners and plating. Finite-element models require discretization ofthe hull into small elements on which the beam and/or plate theory canbe applied. A numerical solution can be obtained providing stress levelson the hull. Proper sizing of the hull, including the water-entrapmentplate can then be confirmed. Additional information about thewater-entrapment plates is disclosed by U.S. Pat. Nos. 7,086,809 and7,281,881 which are both hereby incorporated in their entirety byreference.

With reference to FIG. 10, a top view of the floating wind turbineplatform 105 is shown. In order to keep the floating wind turbineplatform within a desired location, the platform 105 can be anchored tothe seabed using conventional mooring lines. For example, in oneembodiment, the floating wind turbine platform is secured to the seafloor with an asymmetric mooring system. In FIG. 10, six mooring lines131-141 are illustrated. Four mooring lines 131-137 are connected to thecolumn 102 that carries the wind turbine 125, and single mooring lines139-141 are connected to each of the other columns 103. The angularseparation of the mooring lines 131-141 is approximately 60 degreesbetween each adjacent line. The lines 131-141 converge toward a pointlocated at the center of the column 102 supporting the wind turbine 125.The wind will also cause tension in the windward mooring lines connectedto the windward columns to be higher than the tension in the remaininglines.

With reference to FIG. 11, a top view of the floating wind turbineplatform 105 having an alternate mooring configuration is shown. In thisembodiment, four mooring lines 151-157 are used to secure the platformin place. Two lines 151, 153 are coupled to the column 102 supportingthe tower 111, and the moorings 155, 157 are each coupled to one of theother columns 103. In this embodiment, the mooring lines 151-157 areseparated from each other by an angle of about 90 degrees.

With reference to FIG. 12, an elevation of and embodiment of a floatingwind turbine platform 105 as described herein is shown. In theconfiguration shown in FIG. 12, each mooring line 131-141 is angled downand outward from the floating wind turbine platform 105 to the seabedand individually secured and tensioned. The mooring lines 131-141 can betensioned so that the buoyancy of the columns 102, 103 provides an equaltension on each of the lines 131-141 when there is no wind. When thewind blows against the tower 111 and the turbine blades 101, the windloading forces will be transferred to the mooring lines 131-141 and thewindward lines holding the structure against the wind will be under moretension than the downwind lines. The lines 131-141 can be tensioned sothe mooring lines do not rest on the seabed at any time and so that theyextend in a substantially straight path. In an alternativeconfiguration, the mooring lines may be arranged in a similar asymmetricpattern around the platform but only be tightened to a specificsemi-taut tension force so the lines extend in a curved path to the seafloor. With a semi-taut tension system, the mooring lines do not rest onthe seabed in their static equilibrium position with no wind, waves orcurrent.

In yet another embodiment, illustrated in FIG. 13, the structure 105 canbe secured in place with a catenary mooring system with chain lines 402laying on the sea floor. The mooring lines may comprise any suitablematerial, such as, for example, metal chain, wire, polyester orcombinations thereof. In this example, high-holding power drag embedmentanchors 401 are placed into the seabed. The anchors 401 are attached tosections of heavy chain 402 that lay on the seabed. The horizontalorientation of the chain 402 helps to keep the anchors 401 securedwithin the seabed. The chain 402 is connected to a long length ofpolyester line 403 which provides most of the length of the mooring. Thepolyester line 403 provides adequate stretch to the mooring line toprevent high tension spikes from being transmitted from the platform 105to the anchor 401. The polyester line 403 is coupled to another lengthof chain 405 that is attached to the platform 105. The polyester line403 remains suspended in the water and never comes in contact with theseabed after installation. Clump weights 404 may be placed at thejunction between the chain 405 and the polyester line 403 creating asharper bend in the mooring to further reduce tension spikes and ensurethat the line 403 pulls horizontally on the anchor 401. The clumpweights 404 are typically composed of dense materials, such as steel andconcrete and are attached to the bottoms of the top chains 405. Theweigh of the clump weight 404 in water is significantly larger than theweight of the chain 405 to which it is attached.

The chains 405 may pass through the columns 102, 103 to tensioningdevices 407 which allow the mooring line tensions to be individuallyadjusted. The tensioning devices 407 can be, for example, chain jacks,windlasses, winches or other tensioning devices that are mounted at thetop of, along or inside columns 102, 103. In order to prevent damagefrom chafing, fairleads or bending shoes 406 can be positioned at thebases of the columns 102, 103 that allow the passage of the mooringlines through the water-entrapment plates 107. After the tension hasbeen properly set, the mooring lines can be locked.

The wind turbine is typically designed to operate over a normal range ofwind speeds and directions. The wind blowing against the turbine blades101 and tower 111 will create a drag force that will tend to cause thefloating wind turbine platform 105 to lean away from the wind direction.If the wind is coming from between columns 102 onto column 103, in thedirection as shown in FIG. 15, the torque caused by the turbine blades101 and the tower 111 will tend to push the downwind column 102 into thewater and lift the upwind columns 103 out of the water. Since the winddoes not always blow in the same direction, as already described herein,the wind turbine can be equipped with a yaw mechanism that allows thenacelle 125, hub and blades 101 to rotate about the top of the tower 111into alignment with the wind. However, as the wind direction changes,the direction that the tower 111 leans will also change. The horizontalline 161 in FIG. 12 on the columns 102, 103 indicates the designedfloatation water line. As the wind speed and direction change, the windturbine may utilize an internal active ballast system to counteract thewind induced forces and moments and keep the structure 105 at the designfloatation water line 161 under all steady operating conditions.

Therefore, a wind turbine platform as described herein can include aninternal active ballast system. An example of such a system is describedand illustrated with reference to FIG. 14. In such an embodiment, thecolumns 102, 103 are hollow and house an active ballast system 201 thattransfers water between tanks within the columns 102, 103 to keep theplatform 105 in a vertical upright alignment for optimum powerconversion efficiency. For example, when the wind is blowing towards thetower column 102, a sensor 127 can detect the rotation of the windturbine. The sensor 127 is coupled to a controller 123 that controls thepumps 221 to remove water from the tower column 102 to increase thebuoyancy and add water into the other columns 103 to increase theirweight. In an embodiment, there can be multiple pumps in each columncontrolling an independent water path to the other columns. Industrialaxial flow water pumps are available from Huyundai, South Korea andGlynwed AS, Denmark.

The controller can also adjust the water volumes in the columns 103 thatdo not support the turbine tower 111 to adjust the side-to-side angle ofthe wind turbine. In an embodiment, the columns have sensors 225 thatdetect the volume of water, represented in FIG. 14 by the differentwater depths 203 in each of the columns 102, 103. The active movement ofthe water ballast between columns 102, 103 compensates for the inducedwind forces to keep the platform leveled. Because a substantial amountof water must be pumped between the columns 102, 103 the response timeof the internal active ballast system may be between about 15 to 30minutes. Since the response time may be fairly slow, the active ballastsystem will not typically be designed to eliminate the fast dynamicmotions of the structure 105 due to waves and other fast acting forces.However, the platform is designed to withstand these forces without thebenefit of the ballast system. The active ballast system is designed tokeep the mean position of the platform horizontal and maximize energyproduction by keeping the turbine upright as much as possible.

In an embodiment, the active ballast system can be a closed loop systemconfigured to prevent the possible flooding and sinking of the floatingwind turbine platform 105 by completely isolating the water in theballast system from the surrounding seawater. The active ballast systemmoves the contained water between the columns 102, 103 by electricalwater pumps 221 that cause the water to flow through the main beams 115mounted between each of the columns 102, 103. In such an embodiment, thesurrounding sea water is never allowed into the active ballast system.The water in the active ballast system may be fresh water added atquayside before towing, or using a supply boat, to mitigate corrosionproblems and other seawater related issues.

In an embodiment, the alignment sensor 127 includes gyroscopes mountedalong the X axis and Y axis. The gyroscopes output a signal thatrepresents the angular rate of rotation which can be in units of degreesper second. An integration of the angular rate of rotation will producean angular position. Thus, the gyroscopes in the alignment sensor 127can be used to measure variation in the alignment of the platform andtower. The X axis gyroscope is in the horizontal plane and can bealigned with center line of the floating wind turbine platform. The Yaxis accelerometer is also in the horizontal plane but perpendicular tothe X axis gyroscope. The trim angle θ is the angle to the structureabout the Y axis and the list angle φ is the angle of the structureabout the X axis. When the structure is perfectly aligned, the X and Yaxis gyroscope will not detect any acceleration. However, if thestructure leans in any direction, the X axis gyroscope will detect trimrotation and the Y axis gyroscope will detect list rotation. Based uponthis information, the angle of rotation can be calculated using knownmathematical equations.

With reference to FIGS. 15-17, an example of how the active ballastsystem can react to variations in the wind velocity is illustrated.Based upon the alignment sensor signals, the ballast controller cancontrol the pumps to adjust the water volume 191 within each of thecolumns 102, 103 to correct the vertical alignment angular offset. Whenthe platform 105 is within the acceptable horizontal angle, the ballastsystem will stop moving water between the columns 102, 103.

In FIG. 15, the floating wind turbine platform 105 is illustrated in avertical alignment with the wind blowing over the centerline of theplatform 105. The water volume 191 within the cylinders 102, 103 hasbeen properly adjusted for the wind, current wind velocity and winddirection. In FIG. 16 the wind velocity has increased and the increasedwind force has caused the floating wind turbine platform 105 to rotatein pitch. The alignment sensor detects the trim rotation, and thecontroller actuates the pumps to move water from the tower supportedcolumn 102 to the other columns 103. In FIG. 17, the floating windturbine platform 105 has returned to a horizontal alignment tocompensate for the force induced by the increased wind velocity. Becausethere is less water volume 191 in the tower support column 102, there ismore buoyancy at the tower end of the platform 105. Conversely, thehigher volume of water 191 in the other columns 103 further assist inrotating the platform 105 in trim to an upright alignment.

The active ballasting system will also adjust the water in the columns102, 103 when the wind has shifted. With reference to FIGS. 18-20, thefloating wind turbine platform 105 is illustrated with the wind blowingat a 90-degree shift from the platform centerline wind direction, withthe wind coming over the left side of the platform 105. The activeballast system has moved water from the right side column tank 191 tothe left column tank 191 and the platform 105 is substantiallyhorizontal. With reference to FIG. 19, the wind velocity has dropped andthe platform 105 has changed in its list angle. The alignment sensordetects the list angle of the platform 105 and the controller instructspumps 221 to move water from the left column tank 191 to the rightcolumn tank 191. With reference to FIG. 20, the active ballast systemhas moved water from the left column tank 191 to increase the buoyancyand added more water to the right column tank 191 to increase the weightof the column. The platform 105 is again horizontal and the pumps havestopped until the alignment sensor detects another change in theplatform alignment.

The floating wind turbine platforms described herein have differentmodes of operation based upon the ambient conditions. The platform canbe permanently moored using an anchoring system made of a chain jack,chain and wire sections, and an anchor. In such an embodiment, thefloating wind turbine platform will not be moved or disconnected fromthe moorings in case of extreme weather conditions. The main purpose ofthe floating wind turbine platform is to generate electricity, thereforeit can be designed to maximize the amount of time the turbine isoperational.

Since existing turbines stop operating at 25 m/s wind speed, it isdesirable for the wave-induced motions typical of higher wind speeds notto interfere with this operational limit. That is, with reference toFIG. 6, as the structure moves due to the wave forces, the tower 111rotates in trim which causes the top of the tower 111 to movehorizontally and causes variations in the apparent wind against theturbine blades. If the structure 105 rotates into the wind, the top ofthe tower 111 will detect a faster wind speed and conversely if thestructure 105 rotates away from the wind, the top of the tower 111 willdetect a slower wind speed. A wind turbine platform as described hereinreduces the rolling motion by utilizing water entrapment plates 107fastened to the bottoms of the columns 102, 103, which resist verticalmovement and dampen the roll and pitch movements of the platform 105.

Generally, there are three separate turbine blade regimes for the windturbine delineated by the wind speed. In the first regime at wind speedslower than 12 meters per second, the blades are optimized to maximizeelectricity production. In the second regime at wind speeds between 12and 25 meters per second, the blades are actively rotated (pitched) toreduce the loading on the blades and maintain a constant optimalrotational velocity. In the third regime at wind speeds over 25 metersper second, the whole wind turbine is locked down, in a “survival” mode.In the lock down conditions, the turbine blades may be completelystopped and the blade angle is feathered to a minimal drag conditionrelative to the wind. Because the wind velocity and direction can changevery quickly, the third regime may occur very quickly. Thus, the windturbine must be able to quickly and accurately detect and respond towind variations.

In addition to high wind shut down procedures, other conditions maytrigger an emergency shutdown (ESD) which is intended to preserve thefloating wind turbine platform and minimize the loss of equipment. Sincethe platform is normally unmanned, both automated and remote shut downprocedures must be in place. Various system failure or error conditionswill trigger the ESD. For example, a failure of the active ballastsystem can be detected by either a large mean list and or trim anglesthat do not diminish and/or abnormal power requirement of the pumps.Another system failure can be caused by a water leak in a column. Thisfailure can be detected by a list or trim of the platform towards theleaking column, which cannot be compensated by the functioning activeballast system. The system should also be shut down if the turbineblades are subjected to stresses above a threshold level. This failurecan be detected by strain gauges mounted on the blades. Another failureis the inability of the nacelle to rotate the turbine blades into thewind. This can be noted by a discrepancy between the measured winddirection and the nacelle heading. The system can also be shut down whenthere are power failures or a loss of communication between the floatingwind turbine platform and the remote operator.

The wind turbine platforms described herein are designed to beeconomically fabricated, installed and commissioned/decommissioned. Forexample, in order to minimize construction costs, the structure can bedesigned to minimize welding at the assembly yard by providing largepre-assembled cylindrical sections of the columns, which can efficientlyby fabricated in a workshop using automatic welding machines. Thefabrication can be completed in the vicinity of a waterway that is deepenough to allow for the floating wind turbine platform to be towed. Thetower, nacelle and turbine can be installed at quayside at a facilityhaving a large crane. By installing all components at quayside, there isless cost and less risk of damage compared to placing the tower andturbine onto a floating platform in open water.

FIGS. 21-23 illustrate a method for towing the floating wind turbineplatform 105 to the installation site from the fabrication site. Withreference to FIG. 21, the tower 111, nacelle 125 and turbine blades 101are fully assembled with the platform 105 at quayside duringfabrication, and once completed, the platform 105 is towed to theinstallation site with a tugboat. Because most boat yards have a fairlyshallow water channel, the water ballast can be removed from the columns102, 103 so that the platform 105 assumes a minimum transit draft. Thefloating wind turbine platform 105 is stable at its transit draft. Sincethere is more weight supported by the tower column 102, this side of theplatform 105 will normally have a deeper draft, which can be problematicif the water channel from the assembly facility is shallow.

With reference to FIG. 22, where needed, in order to correct the deeperdraft of the tower column 102, a temporary buoyancy module 291 may beattached to the tower column 102, so each of the columns 102, 103 havethe same minimum draft. In other embodiments, temporary buoyancy modulescan be attached to the other columns 103 to further reduce the draft ifnecessary to float the platform 105 through a shallow channel.

With reference to FIG. 23, once the platform 105 is in deeper water, thebuoyancy module is no longer needed and can be removed. The columns arethen ballasted with water down to an even keel with a desired draft,such as, for example, a draft of approximately 50 feet (15 m). Althoughthe deeper draft will increase the hydrodynamic drag, with the waterballasting the platform 105 is much more stable.

The transit route from the fabrication site to the installation siteshould be as short as possible. Thus, the location of the fabricationsite can be project specific. This is especially important when a largeoffshore wind farm comprising multiple floating wind turbine units isbeing constructed and each hull has to be towed a long distance to thewind farm site. The selection of a suitable installation vessel is alsofundamental to the wind farm project economics. The vessel used to towthe wind turbine should also be able to perform mooring installation andmaintenance operations.

The quayside assembly has many advantages over systems that requireassembly at the installation site. More specifically, fixed offshorewind foundations that are attached directly to sea floor require theturbine structure to be installed and maintained at the offshoreinstallation site, which can be difficult and costly. Because it is verycostly to disassemble, substantially all repairs must be done at theoffshore installation site. In contrast, the floating platformconfiguration only requires deploying and connecting the mooring linesto the platform 105. In the case of an unexpected failure of the windturbine, the installation sequence can be reversed, and the platform 105towed back to a port for repairs.

The floating wind turbine platform also simplifies the offshorecommissioning phase. The mooring system needs to be pre-laid and readyto be connected when the floating wind turbine platform is towed to thesite. The wind turbine can be moored by an anchor-handling vessel. Themooring procedures can include recovering the messenger lines attachedto the mooring lines from the platform and pulling in the chain sectionof the mooring line. The connection of the chain to the wire section ofthe line can be done above the water. The tensioning of the mooringlines can be done from the platform with chain jacks. Since the turbineis already installed, the procedure involved to start up the windturbine is also much simpler and less expensive than a wind turbine thatrequires assembly on site.

Because the floating wind turbine platform is a dynamically movingstructure, it is important to minimize the load forces applied to thepower cables connecting the electrical generators to the power station.Once the floating wind turbine platform is properly moored, theprior-installed shore power cable can be connected to the floating windturbine platform. With reference to FIG. 13, in an embodiment, a powercable 501 is coupled to the electrical switchboard on the platform 105.The cable runs down the length of the column 102 in a protective housingand exits near the bottom of the column 102. The switch gear can also bemoved from the tower 111 to the deck 119. In this case the power cablewill run down column 103. The sub sea cable 501 needs to be stable andprotected with covering such as a sheath and/or trenching to preventdamage. Rather than running the cable 501 straight down to the seafloor, the cable 501 can be surrounded by a plurality of buoyancymechanisms 505 to a portion of the cable 501 adjacent and below thelowest portion of the platform 105. This portion of the cable should below enough in the water to prevent any potential contact with shipstraveling in the area. Although the platform 105 is secured with mooringlines, it may not be absolutely fixed in place. The platform can move inresponse to various external forces, including high winds, strongcurrent and rising/falling tides. The lazy wave buoyancy mechanisms 505allow the cable 501 and platform 105 to move without any damage to thecable 501. From the lazy wave buoyancy mechanisms 505 the cable 501 runsto the sea floor and can be buried within the sea floor or a protectiveshell(s) may be placed around the cable 501.

In an embodiment, a plurality of floating wind turbines platforms can bearranged in an array. With reference to FIG. 24, an exemplaryarrangement of asymmetric floating wind turbines platforms 105 in a“wind farm” is illustrated. Since the wind velocity is reduced and madeturbulent when it flows through a wind turbine, in one embodiment, thewind turbines are separated by a radius 355 of about 10 wind turbinerotor diameters or more and arranged in multiple staggered lines 329,331, 333 that are perpendicular to the most frequent wind direction 335.In the illustrated embodiment, the wind turbines 105 are equallyseparated from six adjacent wind turbines 105 by 10 turbine diameters.Because of the staggered configuration, the wind blowing between twofloating wind turbines platform 105 in the first row 329 will have aclear path to the floating wind turbines platforms 105 in the second row331. This wind path will be clear even if the wind direction has shiftedup to 30 degrees away from the preferred direction. The floating windturbines platform 105 in the third row 333 may be in line with thefloating wind turbine platforms 105 in the first row 329, however, sincethere is a separation of about 17 turbine rotor diameters, the loss ofpower due to up wind turbulence is negligible. Even if the winddirection shifts to an angle that aligns the adjacent floating windturbine platforms 105, a 10 turbine rotor diameter separation will onlyhave a minimal effect on power output.

In order to minimize the electrical power cables used by the floatingwind turbine platforms 105, a first cable 341 couples the floating windturbine platforms 105 in the first row 329, a second cable 343 couplesthe floating wind turbine platforms 105 in the second row 331 and athird cable 345 couples the floating wind turbine platforms 105 in thethird row. The three cables 341, 343, 345 are then connected to a fourthcable 347 that transfers all of the electrical power to a power station351, which distributes the electrical power as necessary. In anembodiment, one of the platforms 349 can be used as a power distributionunit and provide for crew and maintenance quarters. This can provide asafe sheltered area where workers can live temporarily and be protectedfrom severe ambient weather conditions.

In another embodiment, individual cables from each turbine are coupledto a junction box on the seabed. There can be a certain number ofconnections per junction box. Larger cables from all the connectionboxes are coupled to a main hub, which is connected to shore using asingle power line. Redundant cables in case of failure can be added tothe power grid infrastructure.

In certain, specific embodiments, a difference between the wind turbineplatforms described herein and those known in the art is the asymmetricconfiguration of the turbine tower that is mounted directly over one ofthe columns. This configuration keeps the majority of the wind turbinemass at the outer edges of the structure rather at the center of thestructure. For example, the “Force Technology WindSea” floating windturbine structure illustrated in FIG. 4, has three towers and turbineblades that are each mounted on a different cylinder. As discussedabove, it is well known that efficiency of the wind turbine is reducedwhen there is turbulence caused by other closely spaced turbine blades.The turbulence and uneven air flow can also induce vibration into thewind turbine system which can prevent the normal operation of the windturbines. The asymmetric wind turbine platform described herein preventsthese problems by utilizing a single tower and turbine bladeconfiguration. Another prior art floating wind turbine system is the“Tri-Floater” illustrated in FIG. 5, illustrates a tower mounted at thecenter of three columns. In order to support this weight, a substantialamount of material is required at the center of the structure. Thisincreases the fabrication time, cost and material required to producethis floating wind turbine platform design and increases the weight atthe center of the structure. By placing much of the mass at the centerrather than at the outer edges less inertial force is required to causethe floating wind turbine platform to roll. In contrast, the asymmetricfloating wind turbine platform described herein simplifies theconstruction by mounting all of the wind turbine components over one ofthe columns so that additional support structures are not required.Also, by moving the mass outward in such an embodiment, the inertialstability is improved.

A single tower mounted over one of the columns in the wind turbineplatforms described herein leads to asymmetric loading of the platform,as the dominant force contribution, which in most conditions will comefrom the wind turbine, is applied to the corresponding column, asopposed to near the center of mass of the platform. An asymmetricmooring system can be used with these asymmetrically loaded platforms,wherein the number of mooring lines connected to the column with thetower is substantially larger than the number of lines connected to theother columns.

As wind turbine technology improves, the size of the wind turbine hasincreased. In one embodiment, a wind turbine platform as describedherein is intended to support a 400 foot diameter wind turbine rotorthat drives a 5 mega watt electrical generator. The estimated componentweights for this wind turbine are listed below in Table 1.

TABLE 1 Mass in Mass in Component Short Tons Metric Tons Rotor 120 130Nacelle 250 280 Tower 380 420 Columns 2500 2800 Ballast water 4000 4500

The estimated sizes of the components of a wind turbine platformsupporting a 5 mega watt electrical generator are listed below in Table2. In other embodiments, the weights and sizes of the floating windturbine platform components can be substantially different than thevalues listed in Tables 1 and 2.

TABLE 2 Dimension Dimension Component in Feet in Meters Tower diameter26.25 8 Tower height 300 91 Rotor diameter 400 126 Clearance betweencolumn and 16.4 5 turbine blade Distance between column centers 200 61Water-entrapment plate width 70 21 Column diameter 30 9 Column height100 30 Draft depth below water line 65 20 at installation Draft depthbelow water line 20 6 quayside

It will be understood that the inventive system has been described withreference to particular embodiments; however additions, deletions andchanges could be made to these embodiments without departing from thescope of the inventive system. For example, the same processes describedcan also be applied to other devices. Although the systems that havebeen described include various components, it is well understood thatthese components and the described configuration can be modified andrearranged in various other configurations.

What is claimed is:
 1. A floating wind turbine platform comprising: a)at least three stabilizing columns, each column having an upper and alower end, and an internal volume for containing a ballast; b) a towerhaving an upper end and a lower end that is coupled to the floating windturbine platform, the tower is mounted in vertical alignment over one ofthe columns and the other columns are not directly under the tower; c) aturbine rotor coupled to an electrical generator, the turbine rotor andthe electrical generator are mounted proximate to the upper end of thetower; d) main beams interconnected to the at least three stabilizingcolumns; e) water-entrapment plates, each of the plates attached to thelower end of one of the stabilizing columns; and f) a ballast controlsystem including an alignment sensor configured to detect a rotation ofthe tower, and a controller coupled to the alignment sensor, thecontroller configured to direct a transfer of the ballast from aninternal volume of one of the columns to an internal volume of at leastone of the other columns upon the alignment sensor detecting rotation ofthe tower to adjust a vertical alignment of the tower.
 2. The floatingwind turbine platform of claim 1 wherein the main beams comprise first,second, and third top main beams, and first, second, and third bottommain beams, and wherein the first top main beam extends between an upperend of the one of the columns over which the tower is mounted and anupper end of a first other column, the first bottom main beam is belowthe first top main beam and extends between a lower end of the one ofthe columns and a lower end of the first other column, the second topmain beam extends between the upper end of the one of the columns and anupper end of a second other column, the second bottom main beam is belowthe second top main beam and extends between the lower end of the one ofthe columns and a lower end of the second other column, the third topmain beam extends between the upper end of the first other column andthe upper end of the second other column, and the third bottom main beamis below the third top main beam and extends between the lower end ofthe first other column and the lower end of the second other column. 3.The floating wind turbine platform of claim 1 wherein the ballastcontrol system further includes: i) a processor for sending andreceiving ballast control signals; ii) a ballast pump in communicationwith the processor for moving the ballast, and wherein the alignmentsensor in communication with the processor detects the verticalalignment of the tower relative to a gravitational force direction. 4.The floating wind turbine platform of claim 3 wherein the ballastcontrol system further includes: iii) ballast volume sensors fordetermining the amount of ballast contained within the internal volumesof the at least three stabilizing columns.
 5. The floating wind turbineplatform of claim 3 wherein the ballast control system is a closed loopsystem.
 6. The floating wind turbine platform of claim 3 wherein theballast control system alignment sensor includes a plurality ofgyroscopes.
 7. The floating wind turbine platform of claim 6 wherein theballast control system alignment sensor plurality of gyroscopes includean x-axis gyroscope mounted in the x-axis direction, the x-axisgyroscope being configured to detect a trim (pitch) rotation, and ay-axis gyroscope mounted in the y-axis direction, the y-axis gyroscopebeing configured to detect a list (roll) rotation.
 8. The floating windturbine platform of claim 7 wherein the ballast control system alignmentsensor plurality of gyroscopes are configured to output a signal thatrepresents an angular rate of rotation, and the controller is configuredto convert the angular rate of rotation to an angular position of thetower.
 9. A floating wind turbine platform comprising: a) at least threestabilizing columns, each column having an upper and a lower end, and aninternal volume for containing a ballast; b) a tower having an upper endand a lower end that is coupled to the floating wind turbine platform,the tower is mounted in vertical alignment over one of the columns andthe other columns are not directly under the tower; c) a turbine rotorcoupled to an electrical generator, the turbine rotor and the electricalgenerator are mounted proximate to the upper end of the tower; d) mainbeams interconnected to the at least three stabilizing columns; e)water-entrapment plates, each of the plates attached to the lower end ofone of the at least three stabilizing columns; and f) a mooringincluding: a plurality of sets of mooring lines, each set coupled to oneof the at least three stabilizing columns lower ends; and a plurality ofanchors embedded in a sea floor and each anchor coupled to one of themooring lines; wherein a number of mooring lines in the set attached toone of the at least three stabilizing columns lower ends is differentfrom the numbers of mooring lines in the sets attached to each of theother stabilizing columns lower ends.
 10. The floating wind turbineplatform of claim 9 wherein for the mooring, a plurality of anglesbetween a plurality of adjacent mooring lines are substantially equal.11. The floating wind turbine platform of claim 9 wherein for themooring, the mooring lines each include: a first section of chain orwire coupled to one of the at least three stabilizing columns; a weightattached to the first section of chain or wire; a section of polyestercoupled to the first section of chain or wire; and a second section ofwire or chain coupled to the section of polyester and one of theanchors.
 12. The floating wind turbine platform of claim 9 wherein forthe mooring, a negative buoyancy of the weight is greater than anegative buoyancy of a first section of chain or wire.
 13. The floatingwind turbine platform of claim 9 wherein the number of mooring linesattached to one of the at least three stabilizing columns is greaterthan one-half of a total number of mooring lines.
 14. The floating windturbine platform of claim 9 wherein the at least three stabilizingcolumns consists of first, second, and third stabilizing columns, theplurality of mooring lines comprises first, second, third, fourth,fifth, and sixth mooring lines, the first, second, third, and fourthmooring lines are attached to the first stabilizing column, the fifthmooring line is attached to the second stabilizing column, and the sixthmooring line is attached to the third stabilizing column.
 15. Thefloating wind turbine platform of claim 9 wherein the at least threestabilizing columns consists of first, second, and third stabilizingcolumns, the plurality of mooring lines comprises first, second, third,and fourth mooring lines, the first and second mooring lines areattached to the first stabilizing column, the third mooring line isattached to the second stabilizing column, and the fourth mooring lineis attached to the third stabilizing column.
 16. The floating windturbine platform of claim 9 wherein the number of mooring lines attachedto the one of the at least three stabilizing columns is greater than thenumber of mooring lines attached to each of the other stabilizingcolumns to support a wind turbine above the one stabilizing column. 17.The floating wind turbine platform of claim 9 wherein the number ofmooring lines attached to the one of at least three stabilizing columnsis two, and the number of mooring lines attached to each of the otherstabilizing columns is one.
 18. The floating wind turbine platform ofclaim 9 wherein an angle between first and second mooring lines attachedto the one of the at least three stabilizing columns is about 90degrees.